The construction of the new "MAREA" cable will begin in August and it is expected to be completed in October 2017, the companies said in a statement on Thursday.
The 6,600 kilometre cable, the first to connect the United States with southern Europe, will be operated and managed by Telefonica SA's (TEF.MC) telecoms infrastructure unit Telxius.
The cable is initially designed to carry 160 terabits of data per second, the companies said.
The move comes nearly two years after Google Inc, now Alphabet Inc (GOOGL.O), agreed with five Asian companies to invest about $300 million to develop and operate a trans-Pacific cable network connecting the United States to Japan. (reut.rs/1P0LEvN)
Microsoft has also been experimenting with underwater data centres under its Project Natick, and last year tested a prototype on the sea floor for four months.
Underwater data centres, envisioned to be powered by renewable marine energy sources, is expected to reduce the huge cost associated with cooling data centres that generate a lot of heat, and also to reduce the distance to connected populations.
Microsoft on Thursday declined to disclose the financial details about MAREA. Facebook did not immediately respond for comment.
Reporting by Kshitiz Goliya in Bengaluru; Editing by Kirti Pandey and Sayantani Ghosh